Abstract
The purpose of this study was to quantify siderophore production by the aerobic bacterium, Pseudomonas mendocina, under Fe-limited conditions as a function of Fe source: supplied in dissolved form (as 30 μM Fe-EDTA), as natural Fe-containing kaolinite, and a no-Fe-added control. Siderophores are Fe(III)-specific organic ligands produced by microorganisms under conditions of Fe stress. Siderophore production was compared with previous experiments wherein Fe was supplied as hematite [Geomicrobiol. J. 17 (2000) 1]. Microbial growth increased in the order: no-added-Fe control<kaolinite<Fe-EDTA. Production of siderophore on a per cell basis decreased in the order: no-Fe-added control>kaolinite>hematite≥Fe-EDTA. Thus, the bacterium was less Fe stressed in the presence of kaolinite than in the no-added-Fe control, confirming that kaolinite serves as a source of Fe to the bacterium. Although more siderophore per cell was produced in the most stressed system (no-Fe-added), more total siderophore was produced in the least stressed system (Fe-EDTA). This is due to the presence of a larger total population size in the least stressed system. Hence, the ability of a microbial population to produce siderophores as a means to access mineral-bound Fe is a complex function of both Fe stress and population size.
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